1. Field of the Invention
The present invention relates to a source driving circuit for a liquid crystal display.
2. Description of the Related Art
Liquid crystal display devices are commonly used in computer monitors, televisions, and view finders. Such devices are typically manufactured by disposing liquid crystal material between a first substrate having a matrix of pixel electrodes and a second substrate having color filters. Source and data driving devices are usually provided in the form of a peripheral circuit. A source driving device may be a digital-to-analog (D/A) converter driver or an analog-to-analog (A/A) driver.
In liquid crystal display devices used in personal computer monitors, especially in multi-media applications, it is difficult to provide images requiring more than 64 grey levels using a D/A driver. A D/A converter devicer in a typical source driver receives n bus lines and can generate 2.sup.n grey levels. As a practical matter, a source driver is limited to providing eight grey levels, since analog switches occupy a large amount of chip area and require relatively large controlling voltages.
It has been proposed to use two eight-grey level source driving devices for a liquid crystal display, in order to provide 64 grey levels. Such a device is shown in FIG. 1. Digital image data on data lines D.sub.0 -D.sub.5 are provided to two 3.times.8 decoders, which operate to select two lines (in this example, lines V.sub.3 and V.sub.5). The average voltage level of the two lines is determined to produce one of 64 grey levels. However, in such an arrangement, there are discontinuities in the voltage distribution between grey levels.